1. Field of Invention
This invention relates to propellers which provide thrust through fluids.
2. Description of Prior Art
The propeller is a common device used to provide the force necessary to move objects trough air and water. Although many variations and improvements have been suggested throughout the years, the basic concept of propellers has remained unchanged. Rotary motion provided by an energy source such as internal combustion, electricity, or manpower causes angled blades to turn, thereby forcing the fluid substantially in a direction, and causing the craft to which the propeller is attached to move in an opposite direction.
Although common propellers at the present time are considered the best method of providing motion for boats through water, they fall far short of having the efficiency which is achieved by aquatic life in the natural world. Propellers may be powerful devices, but much of the energy is wasted on formation of disturbances in the water.
The tail fins of fish and other aquatic creatures provide more thrust with less effort. Designing machines which Approximate fishtail efficiency has proven to be a formidible task. As noted in prior art U.S. Pat. No. 5,401,196, the sweep of a fish tail creates a vortex in water which rotates in a manner which has proven to be invaluable for fish propulsion efficiency. The following stroke reacts with the water movement created by that vortex to create a greater thrust in the forward direction than if the vortex were not present. This cancelling effect between the created vortex and the oncoming fin is believed to be a a factor in high fishtail efficency. At the same time, the following stroke continues the process by creating its own new vortex to be used in a similar manner by a subsequent stroke in the opposite direction. The successive vortices and strokes provide an efficient propulsion method which has yet to be effectively duplicated by a mechanical device.
Even though many efforts have been made to mimic the design of the tail fin of a fish, these designs have been unsuccessful in replacing the common propeller in providing acceptable thrust for watercraft. Because of design improvements of rotary motors producing increased power, propellors have remained the choice for propulsion. The present device utilizes the tailfin action of fishes while incorporating rotary motion provided by any conventional energy source such as electric motors and internal combustion engines. These sources are powerful and reliable, and have been perfected over the years. Since, as will be demonstrated, the motion of the fin is not reversed in the instant device, energy is not wasted in stopping, then accelerating the fin in an opposing direction. Stress on the fin caused by this reversing motion is therefore eliminated. Additionally, since the opposing fins of the instant device present a novel configuration which allows for the immediate reaction of fin and water in a reversed direction, the device closely resembles the action of fishtails. The proposed mechanism simply but effectively combines the advantages of both the common propeller and natural fish-tail motion.
Prior art reveals several disadvantages overcome by the present design. In causing a fin to flap back and forth, devices of the prior art must first stop motion in one direction, then accelerate the fin in the opposite direction. Since most mechanical systems are rotational, converting to a flapping motion tends to be complex and inefficient, requiring linkage and other conversion design. This complexity is not present in the instant device. Also, by continual rotation of different blades in opposite directions, no energy is lost in stopping and starting. Since the momentum of the blades is substantially conserved, the energy of motion may be used in subsequent strokes. Frictional losses caused by the interaction between the blades and the water during the non-thrust segment of their rotation are reduced by minimizing the surface area of the blade reacting with the water. A pivoting, folding, rolling, or compressing manuever accomplishes this task and also allows for the bypass of the opposing blades to avoid collision while permitting the opposing blades to alternately occupy overlapping sweep zones.
The present device has many advantages over all prior art. The cited prior art U.S. Pat. Nos. 4,490,119, 4,568,290, 5,000,706, 5,021,015 and 5,401,196 all represent propulsion systems having one or more reciprocating foils, therefore having the associated problems. The instant mechanism represents a novel approach which, rather than vibrate foils, rotates separate foils in opposing directions while allowing collision-free bypass and reducing drag during non-thrust segments of the rotation. A major advantage of this design is that the effective thrust frequencies which may be generated by counter-rotating fins surpass those anticipated for flapping foils effectively, thereby creating a new range of values for fishtail simulation. Most materials, when flapped from side to side under stress, experience fatigue and eventually break down in some manner or another. The blades of the proposed device are not subjected to this abuse since the blades are not flapped. Fishtail motion is still approximated, in that a vortex created by a sweep reacts with a successive sweep in the opposite rotational direction. In order to increase efficiency, parameters such as frequency, fin size, fin shape, fin flexibility, and sweep length are easily adjusted in the instant device. "An Efficient Swimming Machine", a Scientific American magazine article of March 1995 presents a prior art analysis of such parameters. That article also describes a robotic tuna constructed for experimental purposes, and illustrates the complexity of such a device over the proposed mechanism.